Graphites are important as industrial materials because of their useful characteristics such as excellent heat and chemical resistances, high conductivity, etc., and have been widely used as electrode materials for secondary cells, heating elements, structural materials, gaskets, heat resistant sealing materials and the like.
Examples of the conventional graphite to be used for these applications include the following.
(a) Graphite which is mainly composed of natural graphite: It is produced by mixing natural graphite powder or scale with a binder and molding the mixture, followed by sintering. The graphite is not composed of graphite only, but is a mixture of graphite and carbon. PA0 (b) Film graphite: It is produced by a so-called "expand process", in which natural graphite is dipped in a solution mixture of concentrated sulfuric acid and concentrated nitric acid, and then heated to expand an interlayer gap of the graphite, followed by rinsing to remove acid and subjecting to high-pressure press molding to form film graphite. However, this film graphite is inferior to a single crystal graphite in various characteristics, and its film strength is also low. Further, there is problem that a large amount of the acid is required for the production and toxic gas (e.g. SOx, NOx, etc.) is generated. Also, there is a problem that the acid used in the production is not completely removed and the remaining acid exudes when using the graphite to cause metal corrosion.
The electrode for secondary cell using the graphite or carbon is used by bringing lithium into contact with the graphite, forming an interlayer compound which is obtained by inserting lithium between layers of the graphite to cause dedoping/doping to take electric current out. In this case, the cell characteristics are largely influenced by the properties of the graphite or carbon electrode, and are not always good.
Highly oriented graphite has recently been studied as novel graphite. One of them is a so-called "HOPG (Highly Oriented Pyrolytic Graphite)" which is obtained by depositing carbon atoms on a substrate using a hydrocarbon gas by a CVD (Chemical Vapor Deposition) process, followed by annealing. The HOPG is one in which the orientation direction of a crystal is adjusted to one direction. Another highly oriented pyrogenic graphite which is obtained by a different production process is described in Japanese Laid-Open Patent Publication Nos. 3-75211, 4-21508, etc. The graphites can be produced in a short time and have a desired size and excellent physical properties approaching those of a homogeneous single crystal, which causes no problem due to the residual acid described in the above item (b).
Regarding a secondary cell using a conventional graphite and a carbon, the cell characteristics are largely influenced by the properties of the graphite or carbon electrode, and the cell is not superior in cell characteristics.